The present invention is a portable exhaust emissions measurement system for vehicles and, more specifically a Real-time On-road Vehicle Emissions reporting system which continuously measures, displays, and records the quantity of gaseous emissions (HC, CO, CO2, NO, and O2), in grams/miles driven as well as fuel economy, engine and vehicle operating parameters, engine air/fuel ratio, and road grade, all at a user-selectable update rate. The present invention also relates to a flowmeter module for utilization in the system.
The numerical exhaust gas emission standard established by the United States Environmental Protection Agency (EPA) apply to vehicles tested using the Federal Test Procedure (FTP). The FTP is conducted in a laboratory on a dynamometer under controlled environmental conditions where the vehicle is xe2x80x9cdrivenxe2x80x9d over a specific speed-time trace while the emissions are sampled. The same speed-time trace is used in testing all passenger cars and light-duty trucks and ideally represents typical in-use driving. During the test, the dynamometer applies steady-state and inertial loading on the vehicle simulating actual road-loading and dynamic loading encountered on the road for the same vehicle speeds. A constant volume sampler (CVS) is used to dilute the exhaust gas with air in such a way that the diluted gas flow rate is held constant as the vehicle""s exhaust gas flow rate varies and to obtain a proportionate sample of the diluted exhaust gas during each of the three phases of the test. In this way, the sample""s concentration of each pollutant is essentially proportional to the mass emissions of that pollutant.
In the case of vehicles employing heavy-duty engines, such as tractor trailer trucks and city buses, the associated EPA emission standard applies to the vehicle""s engines which are emission tested on an engine dynamometer while operated over the EPA xe2x80x9ctransient testxe2x80x9d. The emissions sampling system and CVS are similar to that described above for passenger cars. But, the engine to be tested is attached to the engine dynamometer which applies a prescribed torque and engine speed. The engine must be removed from the associated vehicle before testing, if installed. Sometimes vehicle-based electronic sensors which are inputs to the engine""s fueling system, such as a vehicle speed sensor, must be left disconnected or must have simulated values during the emissions test. This may lead to emissions measurements which differ from real-world values.
For a manufacturer to obtain a certificate of conformity permitting the sale of a particular family of vehicles or engines, the manufacturer must demonstrate compliance with applicable EPA emission standards. A major part of the demonstration for passenger cars and light-duty vehicles is passing the FTP and/or heavy-duty engines is passing the transient test. Another, and usually opposing, goal for a manufacturer to meet is maximizing vehicle performance or fuel economy. Because the two goals are usually mutually opposed, and since the FTP and transient test are so well defined and repeatable, meeting the certification emissions standards often becomes a process of xe2x80x9ctweakingxe2x80x9d the calibration values used by the vehicle""s electronic fuel injection system until the numerical emissions standards are satisfied with just enough margin to xe2x80x9cpassxe2x80x9d the FTP and maintain xe2x80x9cpassingxe2x80x9d levels for the xe2x80x9cuseful lifexe2x80x9d of the vehicle.
When the calibration for a particular family of vehicles is xe2x80x9ctweakedxe2x80x9d to pass the FTP, test results do not necessarily reflect the vehicular emissions which result from driving the same vehicle on the road even with the same environmental conditions and vehicle speed schedule. The emissions are dependent not only on the speeds, number of miles and grades driven, but also on the particular driver, familiarity with the course being driven, traffic conditions, etc.
It is important for a responsible vehicle manufacturer to know the actual on-road emissions performance of a vehicle under various competing calibrations and designs so they have the opportunity to make environmental considerations one of the parameters by which they choose a final design or calibration. It is also important for emissions regulators to monitor the emissions performance of vehicles from each of the manufacturers on the road. With today""s sophisticated electronic engine controls, road test data is necessary to determine the effectiveness of the FTP and transient test in helping maintain clean air, as well as for estimates of the emissions inventories. It is only by knowing the actual on-road emissions of vehicles that effective policy can be developed regulating those emissions.
To monitor the emissions performance of vehicles on the road, a user-friendly, portable, and easily transferable on-road emissions measurement system is needed. Ideally, installation of such a system would not require modification of the vehicle to be tested. Further, the emissions measurements of any system must agree well with laboratory FTP testing when both systems are operated concurrently.
Vehicular, on-board gas emission monitoring systems are disclosed in U.S. Pat. No. 5,099,680 issued to Fournier et al, U.S. Pat. No. 5,105,651 issued to Gutmann and U.S. Pat. No. 5,709,082 issued to Harris et al. However, none of these prior art on-board systems measures actual exhaust gas flow rate or provides an instrument module which can be easily transferred between vehicles.
U.S. Pat. No. 5,099,680 discloses an on-board system for analysis of a plurality of exhaust gas components (column 3, lines 45-47) and interfaces with the engine computer (column 3, lines 15-18). This prior art system contemplates the calculation of vehicle emissions in grams per mile, apparently based on vehicle speed and engine displacement, as described at column 4, lines 3-20.
U.S. Pat. No. 5,105,651 discloses an on-board system in the embodiment of FIG. 2. Carbon monoxide and hydrocarbon content of the exhaust gas is monitored (column 4, lines 28-30) and exhaust gas analytical data is correlated with vehicle operation as described at column 6, line 42 to column 7, line 23.
U.S. Pat. No. 5,639,957 notes the 30-50% error in calculation of emissions of gaseous pollutants due to the difference between theoretical and actual values for exhaust gas flow. This prior art reference proposes an improved calculation for determination of theoretical exhaust gas flow.
Accordingly, it is an object of the present invention to provide a mobile, on-board emissions testing system which is transferrable between different vehicles, which provides for a real-time determination of mass flow rates of various gaseous pollutants based on the actual exhaust gas flow rate and which requires no modifications to the vehicle to be tested.
It is another object of the present invention to provide such an emissions testing system in which sensors required to come into contact with the exhaust gas are all incorporated into a module which may be detachably mounted on a vehicle and readily transferred from one vehicle to another.
It is a further object of the present invention to provide such a system with the capability for determination of vehicle operating parameters and correlation of those vehicle operating parameters with pollutant mass flow rates in real time.
It is yet another object of the present invention to provide such a system inclusive of a global position system receiver for continuously monitoring vehicle location and for correlating said pollutant mass flow rates with vehicle driving cycle or driving schedule.
In order to achieve the foregoing objects the present invention provides a mobile vehicle, on-board testing system, including a module designed to be detachably mounted on a vehicle to be tested and support means for detachably fixing the module to a body portion of the vehicle. Connection means, preferably including an elastomeric boot, allows for detachably connecting the module to the exhaust pipe of the vehicle, whereby the flow rate of exhaust gas of the vehicle may be detected by a flow sensing element mounted integrally within the module. Also incorporated into the module is a sampling tube located in close proximity to the flow sensing element for continuously sampling the exhaust gas and routing the sampled exhaust gas to a downstream gas analyzer. The downstream gas analyzer detects concentrations of each of a plurality of gaseous pollutants within the exhaust gas, as sampled through the downstream sample tube, i.e. a sample tube located downstream of an exhaust gas after treatment device, e.g. a catalytic converter. A computer serves as a calculating means for calculating mass flow rates for each of the gaseous pollutants based on the detected concentrations and the detected flow rate of the exhaust gas.
Probes for detecting temperature and absolute pressure of the exhaust gas may also be incorporated into the module. It is advantageous to locate such probes as close as possible to the flow sensing element so that all readings correspond to the same exhaust sample at the same time.
In another aspect, the present invention provides the instrument module utilized in the system described above. The instrument module contains, fixedly mounted therein, an element for determination of flow rate of the exhaust gas (hereinafter xe2x80x9cflow sensing elementxe2x80x9d) and the sample tube for continuously sampling the exhaust gas and routing the sampled exhaust gas to a gas analyzer. As noted above, the module may also contain, fixed therein, probes for determination of temperature and absolute pressure of the exhaust gas. The module should include lengths of straight pipe on opposing sides of the probes to provide the necessary upstream and downstream flow paths for accurate sensing. Another optional feature is the provision of flow straightening means, e.g. a plurality of parallel vanes mounted within the module, upstream of the aforementioned instrument probes. For purposes of particulate matter (PM) detection the module would also incorporate a second, open-ended gas sampling tube for feeding a gas sample to a PM analyzer.
The optional particulate matter (PM) detection unit is especially suitable for use with a diesel powered vehicle. The PM detection unit includes at least one filter element for removing particulate matter from an exhaust gas sample, which element may be removed for weighing before and after some predetermined time during which it receives the exhaust gas sample and collects particulate matter therefrom. In an embodiment including the PM detector, a second, open-ended gas sampling tube is fixed within the aforementioned module to provide a sample to the PM detector, independent and separate from the sample provided to the gas analyzer.
Optionally, the system incorporates a second 5-gas analyzer allowing performance of catalytic converter efficiency tests. The gas sample to the primary analyzer is from the vehicle/engine exhaust system downstream of the catalytic converter or other after treatment device. The gas sample to the secondary analyzer is from the vehicle/engine exhaust system upstream of the catalytic converter. By comparing the gas concentrations upstream and downstream of the catalytic converter, the converter efficiency can be determined in real-time. An automotive scan tool may be used to monitor the inputs as sensed by the vehicle""s on-board computer. Examples of sensed parameters typically monitored include engine speed (RPM), manifold air pressure (MAP), throttle position (TPS), oxygen sensor voltage, etc. The user selects which of the parameters to monitor. The values of the selected parameters are then displayed on the same screen as the gas emissions data as well as saved to the same data file (see FIG. 10). The parameter values in combination with the gas emissions data help one to determine under what conditions high exhaust gas emissions (i.e. pollutants) are being generated and lead to an understanding of the cause of the high emissions.
Thus, the present invention is a computer-based emissions measurement system designed to be used on a moving vehicle. It measures the real-time mass emissions (grams) of plural gases, e.g. hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2), and nitrogen oxide (NO). It does this by using a 5-gas analyzer to measure the concentrations of each of the emissions, a modular exhaust gas flowmeter to measure the exhaust gas volume flow rate corrected to standard conditions (by measurement of exhaust gas temperature and pressure), and by knowing the density of each of the emissions.
Vehicle speed and distance traveled is also measured using a global positioning system (GPS) and/or by monitoring the speed signal sensed by the vehicle""s on-board computer. Knowing the distance traveled by the vehicle as well as the real-time mass emissions, the system of the present invention also calculates the emissions in mass per distance traveled (grams per mile) as well as using a carbon balance technique to determine both fuel economy (miles per gallon) and the air/fuel ratio at which the engine is operated. The results of the mass measurements, the gas concentrations, exhaust gas flow rate, air/fuel ratio, fuel economy, etc., are all displayed and updated in real-time on the computer, as well as stored in a data file of the computer.